1. Field of the Invention
The present invention relates to processes for the preparation of free flowing granular products from moisture laden caked materials and, more particularly, to a process for making such free flowing granular product by mixing a water immiscible substance with moisture laden coal fines.
2. Description of the Invention Background
Conventional mining and coal preparation operations and advanced coal beneficiation processes required to meet stringent environmental regulations regarding the ash and sulfur content of coal produce finely ground coal and coal fines containing 15 to 40% free moisture. Coal has an inherent or equilibrium moisture content within its structure. Lower ranking coals are known to have higher inherent moisture contents. In addition to coal's inherent moisture, the coal fines produced from conventional mining and coal preparation and coal cleaning processes have a volume of free moisture adsorbed on the surface of the coal particles. The moisture laden fine coal product is generally referred to as wet cake in the coal industry.
Wet cake is essentially a wet, sticky lumped mass of coal particles (generally less than about 28 mesh) which is extremely difficult to store, handle and transport. It is often blended with larger sizes of drier coal for bulk shipment for use as a fuel. However, only wet cake which meets the specific moisture specifications of the blended product can be handled in this way. It is necessary at times, in order to meet those specifications, to dry the wet cake in thermal driers to reduce its moisture content. Drying operations increase the cost associated with the use of such finely ground coals. The excess fine wet coal that cannot be handled in this manner has frequently been discarded in settlement ponds, exposing the operator to economic penalties.
The dust generated from the transport and usage of finely ground dried coal is potentially explosive. Furthermore, the loss during transport represents an economic loss as well as contributing to environmental pollution.
Extensive research has provided means to produce fine coal slurries which are capable of being handled and stored as liquids. These slurries can be spray atomized for combustion in furnaces. However, slurries of this nature require extensive use of costly chemicals to ensure long term storage without settling and for providing viscosity control for pumping and atomization.
Processes in which oil is added to finely ground coal in the preparation of coal-oil suspensions are disclosed in U.S. Pat. Nos. 4,859,209 and 4,744,797. In U.S. Pat. No. 4,744,797 heavy oil and coal powder are mixed under low shear force of about 50-150 revolutions per minute with an aqueous solution of a water-soluble gelatin or glue in heavy oil. The solution of the water-soluble component disperses the water in the heavy oil.
The use of oil to "wet" dried, crushed coal in order to reduce the dustiness and the tendency of such coal to ignite is described in U.S. Pat. Nos. 4,775,390; 4,828,576; 4,783,200; 4,402,707; and 3,953,927.
In coal-oil agglomeration processes, oil is added to dilute coal-water mixtures (less than about twenty percent coal) under high shear forces to coat each particle of coal with the oil. The high shear mixing forces cause the oil-coated coal particles to adhere to each other to form agglomerates having little or no water remaining. Agglomeration processes are used to recover and beneficiate coal from water streams. U.S. Pat. Nos. 4,396,396 and 4,889,538 are representative of coal-oil agglomeration processes.
The developments to date have not, however, provided a practical means for stabilizing wet cake to an easily transportable, storable and handleable material.
There is a need for a process of treating moisture laden caked coal fines, such as wet cake, to provide a free flowing material that is easy to store, transport and use. There is a further need for a process that will eliminate or reduce the hazards associated with the processing and handling of such materials. Finally, there is a need for a process for stabilizing wet cake for use as a fuel.